[meteorite-list] A Mars Rover's Great Escape

[Ron Baalke]

http://space.com/missionlaunches/050608_after_opportunity.html

A Mars Rover's Great Escape
By Leonard David 
space.com
08 June 2005

The Opportunity Mars rover is on the move again, but it took nearly five
weeks of frustrating work for controllers back on Earth to make it happen.

And now, great care is being taken not to have a repeat performance of
the six-wheeled robot getting bogged down in martian sand dunes within
its zone of exploration at Meridiani Planum. Before a new traverse gets
underway, Mars teams are piecing together as top priority a strategy to
avoid similar dunes in the future.

"When we hit the dune, we were doing what we call a 'blind drive'", said
Steve Squyres of Cornell University in Ithaca, New York and the
principal investigator for the science instruments aboard both
Opportunity and Spirit rovers.

Squyres said a blind drive is one in which ground controllers are not
checking the rate of the rover's forward progress. Not even looking for
obstacles.

"The good thing about blind driving is that it's fast...we can cover a
lot of ground that way. But we can only use it in terrain that we think
is very benign," Squyres told SPACE.com. "Because we had safely driven
over so many other dunes in the past, blind driving seemed appropriate
in this terrain."

But that decision proved wrong. The rover had a run in with soft sand of
a small martian dune.

"There was something different about this dune that got us," Squyres
explained. That sand trap proved to be "a real learning experience!"

Cautious and deliberate driving

There are a number of lessons learned, spurring a bit of rewriting in
the operator's manual for Opportunity as it cruises the open parking
lot-like landscape of Meridiani Planum.

"We definitely will not be doing long blind drives in this terrain for
awhile. Instead, we'll start turning back on many of the safety checks
that we have in our driving software, proceeding much more cautiously,"
Squyres said. "We'll also try to plan our drives so that we stay in the
troughs between the dunes, rather than driving up and over them."

These changes will slow Opportunity's driving down.

It is doubtful, for instance, that the robot will be doing any more of
those over 650-feet (200-meter) treks across Mars anytime soon, Squyres
suggested. "But we feel pretty confident that we can continue to make
good progress using this more cautious and deliberate driving strategy,"
he added.

Taking the "Erebus Highway"

What's the next move for Opportunity?

Squyres said that will depend on how much time the rover team spends on
studying the dune the robot got stuck in. "We're still working out
exactly what we're going to do, so I'm not prepared right now to guess
how long it'll take."

But once that's done, the plan is for the robot to start moving again,
and toward the south.

"We're still very interested in getting to Erebus crater," Squyres said.
The Mars machine is about 1,312 feet (400 meters) from that crater. But
it is less than 395 feet (120-meters) from what's dubbed the "Erebus
Highway".

"This is a feature we've seen from orbit that looks like a strip of
bright material leading toward the crater. Our guess all along has been
that the bright material in the etched terrain is largely exposed
bedrock," Squyres said. If that guess is right, he continued, then the
Erebus Highway is indeed a thoroughfare that may offer relatively safe
and easy driving.

"We don't know for sure that it's rock, though. If it is something else
-- like dust -- then it could be a trap instead of a highway. There's 
no way to be sure from the orbital images," Squyres said.

So the plan - akin to what the rover teams have done in the past -- is
simply to go there and find out.

"If the highway offers safe driving, then it's southward ho and on to
Erebus. If it doesn't, then we'll stop and think," Squyres concluded.

Layered deposits

As Opportunity unstuck itself, on the other side of Mars the Spirit
rover has been busily working at Gusev Crater.

Now over a year-and-a-half after its landing in 2004, Spirit is rolling
through a range of hills labeled the "Columbia Hills."

Spirit wrapped up observations last week on Larry's Outcrop, part of a
series of outcrops -- Methuselah, Jibsheet, Larry's Lookout -- on the
north flank of Husband Hill in the Columbia Hills.

"Part of the work load has been understanding the chemistry and
mineralogy of these outcrops," said Larry Crumpler, a research curator
in volcanology and space sciences at the New Mexico Museum of Natural
History and Science in Albuquerque. He is on the Mars rover science team.

"The outcrops consist of layered deposits, possibly volcanic and
certainly altered. But, because these layers are tilted, the other part
of the work has been trying to get well-determined estimates of the
orientation. These are what geologists refer to as 'strike and dip' - that
is, the azimuth of the outcrop layers and the tilt of the layers,"
Crumpler told SPACE.com.

Field geology on Mars

There are several outcrops, Crumpler said, and it is difficult to draw a
line between the layers in one outcrop, particularly Jibsheet, and
connect it with the layers just examined on Larry's Outcrop.

Mars scientists want to determine if the variations being seen are just
lateral variations in alteration of the same layer or whether they are
looking at bedding lying at different levels - which started out with
different chemistry and mineralogy.

"By knowing the exact orientation we can make projections from one
outcrop to the other," Crumpler said. Geologists do this all the time in
the field on Earth using a compass and inclinometer - reconstructing
stratigraphy [the origin, composition, distribution and succession of
strata in layered rocks or sediments] from several unconnected outcrops,
he noted.

"Doing that on Earth is hard enough, but we are doing it very remotely
on the surface of another planet. We really are doing field geology on
Mars," Crumpler said.